We’ve recently had several questions from the public asking whether this year has been particularly windy compared to others and if there’s any explanation for this. There’s lots of ways at looking at these questions, but the quick answer from our National Climate Information Centre is that – yes, it has been windy this year and a lack of high pressure seems to be to blame. Here Mike Kendon, climate information scientist at the Met Office, takes a detailed look at the questions.

How many calm days?

One way of looking at this is to consider how many days there have been which have not been windy – i.e. calm days – and how this compares with the historical record. The bar chart below counts the number of days each year, for the UK overall, where at least 20 weather stations have recorded a maximum gust speed of 10 Knots (11 mph) or less. This is equivalent to, at most, a gentle breeze, while 20 stations would indicate such conditions fairly widespread for at least 24 hours.

2015 thus far has seen only 8 such days; this being the fewest number of calm days across the UK for at least 20 years – but bearing in mind this covers less than 7 of 12 months of the year so far. However, more notably none of these days have fallen in May, June or July so far.

Chart showing the number of days per year where at least 20 UK weather stations have recorded a maximum gust speed <= 10 Kt (11 mph). 2015 data up to 22 July.

Pressure patterns

Calm days are typically associated with areas of high pressure, which normally bring dry, settled conditions during summer and cold, frosty conditions in winter – but common to both seasons often light winds. Areas of high pressure tend to block the prevailing westerly airflow across the UK. However, the variability of our climate means that some years see more days of high pressure, others see fewer such days.

The first map below shows the mean sea level pressure relative to average across the North Atlantic for the period January to June 2015. Over this 6-month period the pressure has been lower than normal to the north of Scotland but higher than normal to the south-west, resulting in a predominant westerly airflow over the UK, meaning that our weather has often been windy. Although during 2015 there have been some periods of high pressure, for example during March and early April, they have been relatively infrequent, particularly from May onwards. The pressure difference shown on the map between Iceland and the Azores is known as the North Atlantic Oscillation (NAO) index.

Pressure anomaly (difference from 1981-2010 average) in mb for the period January to June 2015 and January to June 2011, based on NCEP / NCAR Reanalysis data. Image provided by the NOAA/ESRL Physical Sciences Division.

Rainfall patterns

A westerly airflow across the UK is generally associated with low-pressure systems from the Atlantic bringing windy conditions and rain-bearing fronts. Since this is the UK’s prevailing wind direction, the north-west is, on average, much wetter than the south-east, being most exposed to this direction. In addition, rainfall here is further increased due to the effect of hills and mountains.

During 2015, the persistent westerly airflow has resulted in this north-west / south-east contrast in rainfall patterns being exaggerated. For example, Achnagart, a weather station in the West Highlands of Scotland recorded 2082mm of rain in the period from 1st January to 22 July 2015, compared to 237mm for the same period at St James’s Park, Central London – 9 times as much.

The map below shows rainfall totals compared to average from January to June 2015. So, this rainfall pattern is consistent with this westerly weather type, absence of prolonged spells of high pressure, and relatively windy nature of 2015 so far.

Rainfall January to June 2015 as % of 1981-2010 average for that period.

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As forecast, Hurricane Gonzalo made landfall over Bermuda on Friday with rain and winds of up to 110 mph causing power cuts, flooding, felled trees and damaged buildings.

The storm has continued in its journey since then, and passed the Canadian island of Newfoundland during Sunday morning.

The remnants of this tropical storm are being caught up in the westerly flow across the Atlantic and will be drawn towards the UK, crossing the country on Monday night and early Tuesday.

By the time Gonzalo crosses the Atlantic, however, it will be a very different system to the hurricane that affected Bermuda.

It will undergo what meteorologists call ‘extra-tropical transition’, which means it loses the warm-core typical of a tropical cyclone and becomes a much more standard Atlantic low pressure system – like we regularly see around the UK at this time of year.

As such the low pressure is expected to produce wind strengths and rainfall amounts which are not unusual over the British Isles during the autumn and winter months.

Whilst there is good confidence that this system will cross the UK on Monday night and Tuesday morning, there is still something to play for in pinning down the exact location of the strongest winds.

The Met Office has issued a weather warning for wind for much of the UK for Tuesday, particularly since the strongest winds look to coincide with rush hour for some locations, leading to possible travel disruption.

You can see details of what to expect in the warnings page on our website. You can stay up to date with all the latest for the windy weather and what to expect for the rest of the week with our forecasts and warnings.

Provisional half-month statistics up to the 15th of January show a continuation of the generally mild and wet theme of the UK’s winter thus far.

The mean UK temperature up to the 15th of January is 5.1 °C, which is 1.5 °C above the long-term (1981-2010) average.

The mild January so far follows on from a mild UK December, which had a mean temperature of 5.7 °C, which is 1.8 °C above the long-term average – making it the eighth mildest December in records dating back to 1910, and the mildest since 1988.

It’s a similar story with UK rainfall. We’d normally expect about 48% of the January average rainfall by the 15th of the month, but the UK has seen 87.9mm so far – which equates to 72% of the January average.

As usual, there are regional varations. England has been particularly wet so far this month, having already seen close to its full-month average, and Wales is not too far behind. Scotland and Northern Ireland, however, are closer to the ‘normal’ amount of rain we’d expect at this stage.

The wet January so far once again follows the theme set in December, which saw 184.7mm of rain – which is 154% of the average for the month.

While this means January, and winter, so far have been mild and wet, it doesn’t mean they will finish that way. We often see half-month or half-season figures which then change dramatically by the end of the period. So the message is, it’s too early to judge how January 2014 or winter 2013/4 will finish up.

The main reason for the mild and wet weather so far is that we have seen a predominance of west and south-west winds, bringing in mild air from the Atlantic – as well as generally unsettled conditions.

The table below shows provisional figures from 1-15 of January, with actual figures so far compared to full-month averages. We would normally expect rainfall and sunshine to be about 48% of the full-month average at this stage.

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5 November 2013 Update – The full month figures are available in our latest blog

Early statistics for October up to the 28th of the month suggest this October is likely to be one of the warmest in records dating back to 1910.

Map showing relative warmth of October temperatures across the UK.

The mean temperature for the UK from the 1st to the 28th is 11.6 °C, which is 2.1 °C above the long-term (1981-2010) average. It’s currently ranked joint fifth warmest in the records, but this could change once the final three days of data have been included.

Mild temperatures were experienced across all parts of the UK – with October currently being in the top ten warmest for England, Wales, Scotland and Northern Ireland. However, it was particularly mild in Wales, with this October currently ranked as the joint warmest on record alongside 2001.

There were no autumn heat waves through October, just a persistence of mild conditions – particularly mild nights – and frost has been rare through the month.

October 2013 is also notable because it was dull and, for most places, relatively wet. Sunshine hours are currently below the long-term average, while rainfall is already above ‘normal’ levels for everywhere apart from Scotland – which is about average.

Below are figures from 1-28 October, and we’ll update on the full-month figures early next week.

Below is a table showing statistics for 1-28 October, and we’ll update with full-month statistics early next week.

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The UK is set to see unsettled weather throughout this week as heavy rain and windy conditions are expected to affect many areas, whilst temperatures will remain mild for the time of year.

We talk about the jet stream quite a bit in the UK because it has such a big influence on our weather, and this week is no exception as it’s playing a leading role in determining the unsettled outlook.

What is the jet stream?

The jet stream is a band of fast moving westerly winds high up in the atmosphere which circle around the pole in the northern hemisphere. It can feature winds of up to 200 knots (230 mph) or more, and these winds tend to guide wet and windy weather systems which come in off the Atlantic.

The jet moves around a fair bit and its position can have a big impact on weather here in the UK depending on where it is.

If the Jet is over the UK or just to the south, we tend to get a lot of wet and windy conditions as it brings weather systems straight to us. If the jet is to the north of us, it guides that changeable weather away to the north to leave the UK with more settled conditions.

What’s the jet stream doing now?

Unsurprisingly given the outlook for this week, the jet is positioned more or less directly over the UK – but it’s the detail of its track which is important.

As you can see from the picture below, the jet currently swoops south from western Canada – moving over the Atlantic before taking a sharp turn north to head over the UK.

Forecast chart showing expected position of the jet stream at 1pm on Tuesday 22 October

This means relatively cool air is being dragged south then over the Atlantic, where warmer seas heat the air from below. This causes the air to warm and rise – creating instability and generating cloud and rain.

By the time weather systems reach they UK they have picked up a lot of rain and relatively warm air, bringing us the wet but mild conditions we are currently seeing.

What’s the weather outlook?

Currently unsettled weather looks set to impact the UK through the week, with heavy rain affecting many areas at times.

There may be more settled conditions on Thursday, and perhaps again on Saturday, but looking further ahead into the start of next week the outlook is for unsettled weather to continue.

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Large parts of the UK have seen very wet and windy conditions over the weekend.

Winds have gusted up to about 70mph in the most exposed locations, with many parts of the country seeing gusts of 40-50mph.

The strongest gust (at a non-mountain site) was 71mph at Mumbles Head in West Glamorgan, Berry Head in Devon was just behind with 70mph.

Leek, Thorncliffe in Staffordshire saw 68mph, Avonmouth in Avon saw 61mph, and two locations on the Isle of Wight also saw 60mph.

Persistent and heavy rainfall has also been widespread across a large part of the country, with some areas seeing a significant proportion of their normal monthly average within a 24-hour period.

The heaviest rainfall has been focused on southern England with Liscombe in Somerset seeing the most rainfall so far, with 48.8mm falling between 1pm on Saturday, 28 April and 6pm today, 29 April.

Hampstead in Greater London saw 39.2mm of rain during the same period, with Wiggonholt in West Sussex seeing 32.4mm and Rothamstead in Hertfordshire seeing 29.8mm. Several other stations across the south saw rainfall at a similar level.

Other parts of the country, particularly in the far north, have seen very little or no rain at all, however.

Looking ahead, there are Severe Weather Warnings in place for both Monday and Tuesday in parts of the UK, so we’d advise people to stay up to date with the latest forecasts and warnings on our website.

Nathan Rao at the Daily Express has reported on Met Office forecasts of severe gales or even storm force winds across parts of the UK today (Warning as 80mph storm roars in with lashing rain). Met Office forecaster Helen Chivers said in the article: “We are looking at much stronger winds than we saw on Sunday, gale-force moving into storm-force in parts which are going to last for most of the day.” You can stay right up to date with the latest weather forecast and warnings on the Met Office website. Many other regional papers have also reported on our forecasts of severe weather.

Following the publication of the Climate Change Strategy for Wales, which has been informed by climate science experts from the Met Office. Speaking about the strategy, the First Minister for Wales was reported by WalesOnline as saying: “There is no doubt that our climate is changing, and that science states the case that human behaviour is to blame for this change. Met Office Chief Scientist followed this sentiment saying to WalesOnline in an article on what experts say about the strategy: “Our climate is changing and we know that some level of change in the future is unavoidable. Only through adaptation policies, firmly grounded in scientific advice, can we ensure that we are best placed to meet the challenges of climate change head-on.”

Finally SouthWestBusiness.co.uk has reported on the latest Met Office forecaster recruitment campaign, in which we are looking for candidates who are “passionate about meteorology” and not only have the scientific skills to predict the weather accurately but also have the customer service skills to deal with our civilian and military customers.